Astronauts who might journey someday to Mars would be subject to significant radiation risks, a NASA Curiosity rover study released Thursday concluded.

Researchers led by Cary Zeitlin of the Southwest Research Institute in Boulder, Colo., said measurements from the space agency's Curiosity rover, which arrived on Mars last year, suggest astronauts would likely receive a significant fraction -- about 15 percent to 20 percent -- of their lifetime recommended allowable radiation dose on a round-trip to Mars. USA Today reported.

On its trip to Mars the Curiosity rover was shielded by the skin of its enclosing spacecraft, which provided about the amount of shielding astronauts could expect on their way to Mars, the researchers said.

On such a mission a constant stream of cosmic rays from outside the solar system would raise an astronaut's lifetime odds of cancer and cataracts, they said.

"The best thing to do is to get there faster," Zeitlin told the journal Science, which published the study.

Once on the Red Planet, astronauts walking on the surface would largely be unshielded from space radiation, which would further increase their exposure and could put Mars visitors near the point of a 3 percent lifetime risk of cancer that NASA uses as a limit for each astronaut's career.

"By our best current estimates, the cancer risks would not be expected to be a 'show stopper,' but there is still a lot we don't know," said radiation expert Sally Amundson of the Columbia University Medical Center in New York, who was not part of the study.